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Déchets verre, waste

An oasis of waste reconverted into ceramic materials

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Transforming industrial waste and unused by-products could make it possible to respond to issues of scarcity for civil engineering resources, recyclability and even reducing use of fossil fuels. Doan Pham Minh, process engineering researcher at IMT Mines Albi, explains several avenues for recycling and reusing materials explored by his work.

One man’s trash can be another man’s treasure. Turning rubbish into resources is the aim of the circular economy. And it is also the issue at the heart of the Innovative Ceramic Materials for Energy Storage and Construction (MACISEB)[1] project, launched in 2019, with the participation of researchers from IMT Mines Albi[2]. “Our objective is to transform inorganic, industrial waste and by-products, which can be found around us, into something that is useful for society,” describes Doan Pham Minh, process engineering researcher. The solutions identified as part of the project will then be transferred to companies in the Occitania region. From finding other uses for unrecyclable waste to replacing raw materials that are running out, the principle of ‘second life’ can be applied to a large range of unexpected situations.

Sand reserve seeks replacement for time to rest and recuperate

The French Agency for Ecological Transition (Ademe) reports that between 27 and 40 billion tons of sand are extracted each year around the world. It can be found in our buildings and windows, as well as our computers. “The demand for this resource is even more critical than that for noble metals. And the reserves are running out so quickly that they are arriving at breaking point,” emphasizes Pham Minh. Extracted from quarries or taken from riverbeds, natural sand is formed by the lengthy process of erosion. Too long, therefore, to meet society’s needs. However, this material is indispensable for the civil engineering sector (its main consumer) and therefore the economic stability of many countries.

Read more on I’MTech: Sand, an increasingly scarce resource that needs to be replaced

This is why the MACISEB project is seeking sand replacement products from inorganic by-products, i.e. industrial waste that is not currently being used. “The idea is not to completely change our means of manufacturing, but to replace a critical raw material using a circular economy approach,” specifies Pham Minh. With his team, the researcher has created resource maps for the entire Occitan territory. He identified and located deposits with high potential and similar properties to sand. He also ensured that these products are sustainable, by noting the quantity and availability of this waste. In this way, multiple candidates were selected, including glass residue.

During the recycling process, glass is ground up into grains fine enough to be reused by glass factories. However, a portion of this glass, too fine, coarse or contaminated, is not reused. “We are recovering this leftover glass to replace part or all of the sand needed to make ceramic bricks or tiles,” specifies Pham Minh. Sand from foundries, slag from blast furnaces, and ashes from biomass thermal power plants are also promising.

Using these materials, researchers have suggested formulas to create bricks and tiles with the same mechanical and thermal properties as those made with clay and natural sand. Moreover, the formulas comply with industrial specifications. The products are therefore guaranteed to be able to be manufactured using equipment that companies already possess, without extra investment. The first bricks will be made in 2022, and then tested by the Scientific and Technical Center for Building (CSTB).

From wind to heat: reusing wind turbine blades

The operating lifespan of a wind turbine is estimated at around twenty years. This means that the first French facilities are now arriving at end-of-life, and there will have to be more dismantling in the coming years. In short, recycling is becoming a major challenge for the wind energy industry. While the parts made from metal (pole and rotor) and concrete (base) recycle well, the blades – made from glass fiber mixed with organic resin – are not so lucky. Another part of the MACISEB project involves researchers recycling this waste into thermal storage materials. “Our objective is to reuse glass fiber from the blades to develop ceramics used by concentrated solar power (CSP) plants,” explains the researcher. This means of energy production transforms solar energy first into heat, then electricity. To do so, it uses systems made up of mirrors that concentrate the sun’s rays at one point, generating extremely high temperatures (from 200 to 1,500°C). The heat is transported by fluid, to propel the turbines and produce. It can be stored in ‘thermal batteries’, to later be released during the night to ensure continuity of service.

At present, thermal power plants store heat using molten salt – a mixture of potassium nitrate and sodium nitrate. “These compounds can also be found in agricultural fertilizer. There is therefore a conflict of use between the two sectors. However, there is currently no commercial alternative that is economically and environmentally viable,” explains Pham Minh. Transforming turbine blades into ceramics would therefore provide a new solution for this sector. With this in mind, researchers are developing materials capable of handling intense, repeated cycles of heating and cooling for multiple years. This solution would eventually make it possible to reuse a waste product that promises to grow. But it will also give a technological boost to the thermodynamic solar energy sector, which could allow it to establish itself in the renewable energy market. As part of the MACISEB project, this research is being undertaken by the PROMES laboratory, a partner of the project and academic reference body in the area of thermal storage. ART-DEV, partner and social sciences laboratory, is also looking into the social conditions for recycling wind turbine blades and the possibility of implementing a recycling ecosystem for the blades at a regional scale.

Industrial fumes: an idea to get the turbines going

Another application could make use of ceramic materials made from inorganic waste to capture heat. At present, the industry squanders over 30% of the energy it consumes in the form of so-called waste heat, released into the atmosphere in industrial fumes. Researchers at IMT Mines Albi are collaborating with company Eco-Tech Ceram, specialist in thermal storage, in order to recover this energy, store it and use it to supply industrial processes. For example, ceramicists and metal-working factories use high-temperature ovens, often running on natural gas. Reusing the heat captured from their fumes would make it possible to partially heat their equipment and therefore reduce their fossil fuel consumption.

Like for thermodynamic solar, the challenge is therefore to develop ceramic materials adapted for companies’ conditions of use. “Nevertheless, here another issue arises: industrial fumes contain pollutants. Such acidic, corrosive gases accelerate the aging of ceramics and therefore alter their performance,” explains the researcher. Moreover, the composition of fumes varies according to the industrial operations. The first thing to do will therefore be to characterize the kind of fumes, their temperature, etc. sector by sector, in order to develop sustainable materials while keeping costs under control[3].

Anaïs Culot

[1] Project funded by the European Regional Development Fund (ERDF), part of European policy aiming to strengthen economic, social and territorial cohesion in the European Union by supporting development in regions such as here, in the Occitania region.
[2] The project brings together researchers from the RAPSODEE center, the PROcesses, Materials and Solar Energy (PROMES) laboratory, the Actors, Resources and Territories in Development (ART-DEV) laboratory and the company Eco-Tech Ceram.
[3] This is part of the objectives of certain projects, Eco-Stock® solutions to recycle complex industrial waste heat (SOLUTEC, launched in 2021) and developing monolithic materials from local clay blends to reuse industrial waste heat in Occitania (CHATO, launched in 2021), led by IMT Mines Albi.

Cleaning up polluted tertiary wastewater from the agri-food industry with floating wetlands

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In 2018, IMT Atlantique researchers launched the FloWAT project, based on a hydroponic system of floating wetlands. It aims to reduce polluting emissions from treated wastewater into the discharge site.

Claire Gérente, researcher at IMT Atlantique, has been coordinating the FloWat1 decontamination project, funded by the French National Agency for Research (ANR), since its creation. The main aim of the initiative is to provide complementary treatment for tertiary wastewater from the agri-food industry, using floating wetlands. Tertiary wastewater is effluent that undergoes a final phase in the water treatment process to eliminate residual pollutants. It is then drained into the discharge site, an aquatic ecosystem where treated wastewater is released.

These wetlands act as filters for particle and dissolved pollutants. They can easily be added to existing waste stabilization pond systems in order to further treat this water. One of this project’s objectives is to improve on conventional floating wetlands to increase phosphorus removal, or even collect it for reuse, thereby reducing the pressure on this non-renewable resource.

In this context, research is being conducted around the use of a particular material, cellular concrete, to allow phosphorus to be recovered. “Phosphorus removal is of great environmental interest, particularly as it reduces the eutrophication of natural water sources that are discharge sites for treated effluent,” states Gérente. Eutrophication is a process characterized by an increase in nitrogen and phosphorus concentration in water, leading to ecosystem disruption.

Floating wetlands: a nature-based solution

The floating wetland system involves covering an area of water, typically a pond, with plants placed on a floating bed, specifically sedges. The submerged roots act as filters, retaining the pollutants found in the water via various physical, chemical and biological processes. This mechanism is called phytopurification.

Floating wetlands are part of an approach known as nature-based solutions, whereby natural systems, less costly than conventional technologies, are implemented to respond to ecological challenges. To function efficiently, the most important thing is to “monitor that the plants are growing well, as they are the site of decontamination,” emphasizes Gérente.

In order to meet the project objectives, a pilot study was set up on an industrial abattoir and meat processing site. After being biologically treated, real agri-food effluent is discharged into four pilot ponds, three of which that are covered with floating wetlands of various sizes, and one that is uncovered, as a control. The experimental site is entirely automated and can be controlled remotely to facilitate supervision.

Performance monitoring is undertaken for the treatment of organic matter, nitrogen, phosphorus and suspended matter. As well as data on the incoming and outgoing water quality, physico-chemical parameters and climate data are constantly monitored. The outcome for pollutants in the different components of the treatment system will be identified by sampling and analysis of plants, sediment and phosphorus removal material.

These floating wetlands will be the first to be easy to dismantle and recycle, improved for phosphorus removal and even collection, as well as able to treat suspended matter, carbon pollution and nutrients.

L’attribut alt de cette image est vide, son nom de fichier est MF-2.jpg.
Photograph of the experimental system

Improving compliance with regulation

In 1991, the French government established a limit on phosphorus levels to reduce water pollution, in order to preserve biodiversity and prevent algal bloom, which is when one or several algae species grow rapidly in an aquatic system.

The floating wetlands developed by IMT Atlantique researchers could allow these thresholds to be better respected, by improving capacities for water treatment. Furthermore, they are part of a circular economy approach, as beyond collecting phosphorus for reuse, the cellular concrete and polymers used as plant supports are recyclable or reusable.

Further reading on I’MTech: Circular economy, environmental assessment and environmental budgeting

To create these wetlands, you simply have to place the plants on the discharge ponds. This makes this technique cheap and easy to implement. However, while such systems integrate rather well into the landscape, they are not suitable for all environments. The climate in northern countries, for example, may slow down or impair how the plants function. Furthermore, results take longer to obtain with natural methods like floating wetlands than with conventional methods. Nearly 7000 French agri-food companies have been identified as potential users for these floating wetlands. Nevertheless, the FloWAT coordinator reminds us that “this project is a feasability study, our role is to evaluate the effectiveness of floating wetlands as a filtering system. We will have to wait until the project finishes in 2023 to find out if this promising treatment system is effective.”

Rémy Fauvel

brominated plastics

Innovative approaches to recycling brominated plastics

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Recovering untreated plastic materials and putting them back into the recycling loop through a decontamination line is the challenge of thesis research by Layla Gripon, a PhD student at IMT Lille Douai. These extraction methods contribute to a comprehensive approach to recovering plastic materials, in particular brominated plastics.

High consumption of electronic devices implies a significant amount of waste to be processed. While waste electrical and electronic equipment (WEEE) is often seen as a gold mine of silver and rare earths, plastic materials represent 18% of these deposits. This was equivalent to 143,000 tons in France in 2018 according to a report by Ademe (Ecological Transition Agency) published in 2019. But not all this plastic material is created equal. Some of it contains atoms of bromine – a chemical compound that is widely used in industrial flame retardants. These substances meet requirements for reducing flammability hazards in devices that may get hot while in use, such as computers or televisions. There’s just one problem: many of these substances are persistent organic pollutants (called POP). This means that they are molecules that can travel great distances without being transformed, and which are toxic to the environment and our health. The amount of these molecules contained in devices is therefore regulated in the design stage, as well as in the end-of-life processing stage. In 2019, the European Union set the threshold at which waste containing bromine can no longer be recycled at 2 grams per kilo. Beyond this limit, it is destroyed through incineration or used as fuel. But couldn’t it still be recycled, with the right processing? For her thesis co-supervised by researchers at IMT Lille Douai and The Alençon Institute of Plastics and Composites (ISPA), Layla Gripon has set out to identify a method for separating brominated flame retardants from plastics. “We seek to maximize recycling by limiting the loss of unrecoverable material, while complying with regulations,” says the PhD student.

Finding the right balance between extraction efficiency and respect for the environment

Approximately 13% of WEEE plastics are above the legal threshold for brominated flame retardants, which is equivalent to 17,500 tons in France. Samples tested in the laboratory reached a concentration of bromine up to 4 times higher than the legal threshold. In order to process them, Layla Gripon tested a number of methods that do not degrade the original plastic material. The first was highly efficient, removing 80% of the bromine. It was an extraction method used diethyl ether, an organic solvent. But since it uses a lot of solvent, it is not an environmentally-friendly solution. Another technique based on solvents is dissolution-precipitation. Through this technique, plastic is dissolved in the solvent, which retains the flame retardants. “In order to limit the environmental impact of this process, we subcontracted the German Fraunhofer Institute to carry out a test. Their patented process (CreaSolv) allows them to reuse the solvents. In the end, the bromine was no longer detected after processing and the environmental impact was reduced,” she explains.

In addition, a method that is more environmentally-friendly – but less efficient, for now – uses supercritical CO2, a green, non-toxic and non-flammable solvent. This process is already used in the agri-food industry, for example, to remove caffeine from coffee. In the supercritical state, carbon dioxide exists in an intermediate state between liquid and gas. To achieve this, the gas is heated and pressurized. In practice, the closed-loop system used by Layla Gripon is simple. Shredded plastic is placed inside an autoclave in which the supercritical fluid circulates continuously. When it leaves the autoclave, the recovered gas brings various additives with it, including a portion of the flame retardants.

To improve the yield of the second method, Layla Gripon planned to use a small amount of solvent. “The tests with ethanol improved the yield, with a rate of 44% of bromine removed, but this wasn’t enough,” says the PhD student. Other solvents could be considered in the future. “The supercritical CO2 method, on the other hand, works very well on the brominated flame retardant that is currently the most widely-used in industry (tetrabromobisphenol A – TBBPA),” she adds. But the most difficult brominated plastics to process are the ones that have been prohibited for a number of years. Although they are no longer available on the market, they are still accumulating as waste.

A large-scale approach to recovering recycled plastic  

These promising processing techniques must still evolve to respond fully to the needs of the recycling industry. “If these two processes are selected for applications beyond the laboratory, their environmental impact will have to be minimized,” says the PhD student. Such methods could therefore be incorporated in the pre-processing stage before the mechanical recycling of WEEE plastics.

At the same time, manufacturers are interested in the benefits of this research initiated through the Ecocirnov1 Chair. “They’ve joined this project because the laws are changing quickly and their products must take into account the need to recover materials,” explains Éric Lafranche, a researcher who specializes in plastic materials at IMT Lille Douai and is Layla Gripon’s thesis supervisor. The objective of maximizing recycling is combined with an ambition to create new products tailored to the properties of the recycled materials.  

Read more on I’MTech: A sorting algorithm to improve plastic recycling

“Recycling today is different than it was 10 years ago. Before, we sought to recover the material, reuse it with similar properties for an application identical to its original use. But the recycled product loses some of its properties. We have to find new applications to optimize its use,” says Éric Lafranche. For example, French industrial group Legrand, which specializes in electrical installations and information networks, seeks to use recycled plastic materials in its electrical protection products. In collaboration with researchers from IMT Lille Douai, the company has implemented a multilayer injection system based on recovered materials and higher-grade raw materials on the surface. This offers new opportunities for applications for recycled plastics – as long as their end-of-life processing is optimized.

By Anaïs Culot.

1 Circular economy and recycling chair created in 2015, bringing together IMT Lille Douai, and the Alençon Institute of Plastics and Composites and Armines.